Uranium induces TNFα secretion and MAPK activation in a rat alveolar macrophage cell line

Uranium is a toxic heavy metal found mainly in the nuclear industry, but it is also used in the manufacturing of military munitions. Inhalation studies using animal models have demonstrated that long-term exposure to uranium can lead to the development of neoplasia and fibrosis at the pulmonary level. Because it has been demonstrated that such effects are often associated with inflammation, the effect of uranium on TNFalpha, IL-1beta, and IL-10 synthesis by macrophages was assessed in vitro using the NR8383 cell line. Our results show that a significant TNFalpha secretion was induced by uranium but not by other metals such as gadolinium. However, IL-1beta and IL-10 secretions were unaffected by uranium treatment. TNFalpha secretion was detectable since 50 microM of uranium and was maximal after 24 h of exposure. Determination of the mechanisms of uranium-induced TNFalpha production was assessed through the evaluation of protein kinases activation. Our results showed that uranium treatment induced c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) activation. The use of pharmacological inhibitors suggested that both p38 MAPK and protein kinase C (PKC) participate in the signal transduction of uranium-induced TNFalpha secretion. The regulation of TNFalpha secretion involves TNFalpha mRNA accumulation at least through the stabilization of TNFalpha mRNA, but p38 MAPK did not appear to be involved in this stabilization. However, this observation does not exclude regulation of TNFalpha synthesis at the transcriptional level, which remains to be demonstrated. Taking together, these results suggest that uranium can induce TNFalpha secretion by macrophages, thus contributing to a better understanding of the pathological effect of uranium on the lung.

Th(1)/Th(2) responses to drugs

T lymphocytes can be characterized by their pattern of cytokine secretion and be divided into type I (Th(l)/Tc(l)) and type 2 (Th(2)/Tc(2)) subsets. The involvement of type-1 or type 2-like responses in sensitization has been studied in the mouse, with reference contact and respiratory contact sensitizers. One interesting feature with certain drugs, such as beta-lactam antibiotics, is the diversity of clinical manifestations associated with immune-mediated hypersensitivity reactions in humans: immediate reactions such as urticaria, Quincke oedema and anaphylactic shock, and delayed hypersensitivity reactions, such as maculopapular rashes, allergic contact dermatitis and skin reactions of other types. In the mouse, Th(1) and Th(2) cytokines have been shown to regulate primary and secondary benzylpenicilloyl- (BPO-) specific antibody responses. Peripheral blood lymphocytes isolated from patients with a clear history of beta-lactam allergy were assessed for type-1 and type-2 phenotypes. Immediate reactions involved mixed Th(1), Tc(1), and Tc(2) responses, whereas allergic contact dermatitis involved Tc(1) and Th(1) cells. Other delayed hypersensitivity reactions to beta-lactams were restricted to Th(1) responses. It has been demonstrated that both CD4(+) and CD8(+)-lidocaine-specific T cell clones isolated from patients with allergic contact dermatitis produced IFN-gamma, even though CD8(+) clones only produce IFN-gamma, while IFN-gamma producing CD4(+) cells concomitantly produced IL-5 and IL-4. Together these data illustrate the heterogeneity of drug-specific T-cell responses.

Il-4 and IFN-gamma mRNA induction in human peripheral lymphocytes specific for beta-lactam antibiotics in immediate or delayed hypersensitivity reactions

Beta-lactam antibiotics elicit CD4+ and CD8+ T-cell-mediated immune responses that play a central role in allergic reactions. However, the involvement of a type 1- (Th1 or Tc1) or a type 2-like (Th2 or Tc2) differentiation in drug allergy remains unclear. We investigated the expression of interleukin 4 (IL-4) and interferon gamma (IFN-gamma) mRNA by quantitative reverse transcription and polymerase chain reaction (RT-PCR) in patient-derived peripheral blood lymphocytes following specific in vitro stimulation. Samples were collected from a total of 19 patients who had developed immediate or delayed clinical manifestations of hypersensitivity to beta-lactam and from 11 control subjects. Peripheral blood mononuclear cells (PBMCs) were stimulated with either free antibiotics or antibiotic-human serum albumin (HSA) conjugates. Specific induction of IFN-gamma mRNA expression was observed in 11 of 11 allergic patients with immediate reactions, in 6 of 8 patients with delayed reactions, and in 4 of 11 control subjects. IL-4 mRNA expression was induced in 5 of 11 allergic individuals with immediate reactions but in none of the 8 patients with delayed responses and none of the 11 control subjects. IL-4 mRNA expression was only induced following activation with free drugs, while IFN-gamma mRNA expression was predominantly induced in CD4+ T cells following stimulation with HSA-conjugated drugs. Immediate-type hypersensitivity to beta-lactams was not associated with a pure type 2-like response when PBMCs were specifically stimulated in vitro: Some patients with well-documented history of beta-lactam-induced immediate allergic reaction showed a high IFN-gamma response. Contact dermatitis involved Tc1 and Th1 cells and other delayed hypersensitivity reactions to beta-lactams were restricted to Th1 responses.

[Principal cellular and molecular mechanisms of xenobiotic-induced hypersensitivity reactions]

Sensitization to xenobiotic first involves an interaction between the compound and antigen presenting cells such as Langerhans cells within the epidermis. This leads to the transdermal migration of this presenting cells towards draining lymph nodes. A second step consists in activation, proliferation and differenciation of CD4+ T cells, and CD8+ T lymphocytes involved in delayed hypersensitivity reactions such as contact dermatitis. T helper lymphocytes can differenciate into Th1 (producing interferon-gamma and interleukin (IL)-2) or Th2 (producing IL-4, IL-5, IL-10, IL-13) lymphocytes. Some experimental models allowed to demonstrate a link between Th1- or Th2-type responses and different hypersensitivity reactions. Specific antibody production also plays a key role in xenobiotic-induced allergy, especially IgE production involved in mastocytes degranulation and immediate hypersensitivity reactions.

Quantitation of cytokine mRNA expression as an endpoint for prediction and diagnosis of xenobiotic-induced hypersensitivity reactions

Xenobiotic-induced hypersensitivity reactions are immune-mediated effects that involve specific antibodies and/or effector and regulatory T lymphocytes. Cytokines are key mediators of such responses and must be considered as possible endpoints for predicting sensitizing potency of drugs and chemicals, as well as for helping diagnosis of allergy. Detecting cytokine production at the protein level has been shown to not be always sensitive enough. This paper describes three examples of the utilization of semiquantitative or competitive reverse transcription polymerase chain reaction analysis of interleukin-4, interferon gamma, and interleukin-1beta mRNAs as endpoints for assessing T-cell or dendritic cell responses to sensitizing drugs (beta-lactam antibiotics) or chemicals (dinitrochlorobenzene).

Mechanisms of drug-induced allergic contact dermatitis

Allergic contact dermatitis is induced by a wide variety of drugs that trigger specific immune responses following topical exposure. Identified chemical structures involved in such reactions include the mercuric and thiosalicylic acid groups of thimerosal, the diphenylketone group of the anti-inflammatory drug ketoprofen, the amide or ester structure of local anesthetics, and the side-chain and thiazolidine ring of beta-lactams. The T cell responses to such compounds involve CD4+ and CD8+ alphabeta+ T lymphocytes and also CD4 /CD8 gammadelta+ T cells. Although "T helper 2" cytokine production by drug-specific human T cells from patients with allergic contact dermatitis has been described, T helper 1-like and T cytotoxic 1-like responses clearly play key roles in this cutaneous reaction.

Testing strategies in immunotoxicology

Developing a battery of immune function assays to screen potential immunotoxic compounds has been a major issue these past years. Improving this approach is possible using new probes and parameters that are now available from recent knowledge on how the immune system is working (apoptosis, RT-PCR for cytokine mRNA expression). Immunotoxic outcome generally results in serious adverse effects, thus it seems appropriate to evaluate this risk early in drug development. This is especially true in the context of the emerging combinatorial chemistry techniques and high throughput screening in pharmacology resulting in probably numerous molecules to test in toxicology. In this case, screening for adverse effects (genotoxicity, hepatotoxicity, immunotoxicity) that may compromise definitely the development of a molecule should be a help in the decision process since more than one molecule with equivalent pharmacological properties may be available.

IL-4 in Combination with TGF-β Favors an Alternative Pathway of Th1 Development Independent of IL-12

IL-4 was found to be the essential differentiation factor for Th2 cells and simultaneously to be a potent inhibitor of Th1 development that is induced by IFN-γ and IL-12. Furthermore, it was demonstrated that TGF-β can also inhibit Th1 development. In this work, we demonstrate that polyclonal activation of Mel-14highCD4+ T cells by immobilized anti-αβTCR mAb together with a mixture of IL-4 and TGF-β can lead to the development of both Th1 and Th2 cells, depending on the concentration of these cytokines. Additional experiments revealed that Th1 induction by a combination of IL-4 and TGF-β depends on the presence of endogenous IFN-γ, and that this alternative Th1 development is further enhanced by IL-12, but is not dependent on this cytokine. Moreover, naive OVA323–339-specific Th cells that were stimulated by APCs and OVA323–339 peptide differentiated toward Th1 cells after priming in the presence of IL-4 in combination with TGF-β. Hence, this finding confirmed the results obtained by polyclonal activation of naive CD4+ Th cells and implicates that this alternative Th1 development may also occur in vivo under the influence of TGF-β and IL-4 independently of the Th1-promoting effect of IL-12.

IL-4 in combination with TGF-beta favors an alternative pathway of Th1 development independent of IL-12

IL-4 was found to be the essential differentiation factor for Th2 cells and simultaneously to be a potent inhibitor of Th1 development that is induced by IFN-gamma and IL-12. Furthermore, it was demonstrated that TGF-beta can also inhibit Thl development. In this work, we demonstrate that polyclonal activation of Mel-14highCD4+ T cells by immobilized anti-alphabetaTCR mAb together with a mixture of IL-4 and TGF-beta can lead to the development of both Th1 and Th2 cells, depending on the concentration of these cytokines. Additional experiments revealed that Th1 induction by a combination of IL-4 and TGF-beta depends on the presence of endogenous IFN-gamma, and that this alternative Th1 development is further enhanced by IL-12, but is not dependent on this cytokine. Moreover, naive OVA323-339-specific Th cells that were stimulated by APCs and OVA323-339 peptide differentiated toward Th1 cells after priming in the presence of IL-4 in combination with TGF-beta. Hence, this finding confirmed the results obtained by polyclonal activation of naive CD4+ Th cells and implicates that this alternative Th1 development may also occur in vivo under the influence of TGF-beta and IL-4 independently of the Th1-promoting effect of IL-12.

Cyclosporin-A inhibits human endothelial cells proliferation through interleukin-6-dependent mechanisms

Cyclosporine A (CsA) is a widely used immunosuppressant which possesses significant side effects including nephrotoxicity and systemic arterial hypertension. In this work we evaluated the effects of CsA on human umbilical endothelial cell proliferation (HUVEC). Treatment of endothelial cells with CsA inhibited cell proliferation, and was correlated with an increase of interleukin-6 (IL-6) production and IL-6 mRNA expression. Addition of exogenous IL-6 also significantly altered cell proliferation. Furthermore, neutralization of endogenous IL-6 with a specific monoclonal antibody concomitantly with CsA treatment completely restored HUVEC proliferation. These results suggest that CsA-induced inhibition of HUVEC proliferation is mediated through an augmentation of IL-6 synthesis.

Interleukin-10 and interleukin-4 have similar effects on hapten-specific primary antibody responses to penicillin in vivo

Interleukin (IL)-10 was initially recognized on the basis of its capacity to inhibit production of interferon (IFN)-gamma by T helper (Th)1 lymphocytes; we examined whether this cytokine can bias the primary antibody (Ab) response to the hapten penicillin. We previously reported that BALB/c and SJL mice develop different responses to benzylpenicillin coupled to tetanus toxoid (BPO-TT). The response of SJL mice was characterized as Th2 on the basis of early and high IL-4 mRNA expression and production of BPO-specific Ab of the IgG1 isotype. In contrast, the response of BALB/c mice was characterized as Th1 on the basis of delayed and weaker IL-4 mRNA expression associated with high anti-BPO IgG2a production (Kerdine, S. et al., Mol. Immunol. 1996. 33: 71). In this report, we demonstrate that in naive animals, the level of expression of IL-10 mRNA in LN cells was high in SJL and barely detectable in BALB/c. In addition, injection of BPO-TT resulted in rapid and large increase of IL-10 mRNA expression in SJL. Neutralization of IL-10 in vivo promoted the production of BPO-specific IgG2a in SJL, and injection of IL-10-CHO cells inhibited BPO-specific IgG2a production in BALB/c. Neutralization on administration of IL-10 had effects very similar to neutralization or administration of IL-4. However, co-neutralization of IL-10 and IL-4 in SJL did not evidence additive or synergistic effects of the two cytokines. Administration of IL-10 or IL-4 in BALB/c inhibited BPO-TT-induced expression of IL-12 p40 mRNA without modulating IFN-gamma mRNA. Together, these data demonstrate that endogenous production of IL-10 regulates the production of IgG2a Ab in response to BPO-TT and that IL-10, like IL-4, is critical for controlling primary responses to antibiotics which behave as haptenic compounds.

Interleukin-4 plays a dominant role in Th1- or Th2-like responses during the primary immune response to the hapten penicillin

Despite a large number of studies on the Thl/Th2 balance during immune response to pathogens or protein antigens, little is known concerning the early events which regulate Thl/Th2 differentiation following a single injection of haptenic compounds. In this work, we studied how two mouse strains with different MHC haplotypes, SJL (H-2s) and Balb/c (H-2d), could develop different primary immune responses to subcutaneously injected benzylpenicillin coupled to tetanus toxoid (BPO-TT). The SJL mice showed a high BPO-specific IgG1 response that was maximum on day 10 and no BPO-specific IgG2a response. In contrast, Balb/c mice showed a high BPO-specific IgG2a response on days 15 and 22 and a weak IgG1 production. In SJL mice, the response to BPO-TT was characterized by a very early and high IL-4 mRNA expression. In Balb/c, a delayed and weaker expression of IL-4 mRNA was observed. Kinetics of IL-2 and IFN-gamma mRNA expression were comparable in both strains, but IFN-gamma mRNA expression was higher in SJL than in Balb/c. In vivo neutralization of IL-4 induced a significant BPO-specific IgG2a production and a two-fold reduction of IgG1 production in SJL mice while it accelerated production of BPO-specific IgG2a in Balb/c mice. In addition, studies of IL-12 p4O and IL-10 mRNA expression following immunization with BPO-TT showed a greater IL-12 p4O mRNA expression in Balb/c mice and a slightly higher IL-10 mRNA expression in SJL. Taken together, our data suggest that Th1 or Th2 differentiation in primary immune responses to haptenic compounds such as penicillin may be driven by the kinetics and the level of IL-4 production rather than by the level of IFN-gamma. Additional cytokines such as IL-10 and IL-12 are likely to contribute to the regulation of this response.